Lighting system with power factor correction control data determined from a phase modulated signal

ABSTRACT

A light emitting diode (LED) lighting system includes a power factor correction (PFC) controller that determines at least one power factor correction control parameter from phase delays of a phase modulated signal. In at least one embodiment, a peak voltage of the phase modulated signal is a PFC control parameter used by the PFC controller to control power factor correction and generation of a link voltage by a PFC LED driver circuit. The phase delays are related to a peak voltage of the phase modulated signal. Thus, in at least one embodiment, detecting the phase delay in one or more cycles of the phase modulated signal allows the PFC controller to determine the peak voltage of the phase modulated signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) and 37C.F.R. § 1.78 of U.S. Provisional Application No. 60/894,295, filed Mar.12, 2007 and entitled “Lighting Fixture.” U.S. Provisional ApplicationNo. 60/894,295 includes exemplary systems and methods and isincorporated by reference in its entirety.

This application claims the benefit under 35 U.S.C. § 119(e) and 37C.F.R. § 178 of U.S. Provisional Application No. 60/909,458, entitled“Ballast for Light Emitting Diode Light Sources,” inventor John L.Melanson, and filed on Apr. 1, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety.

U.S. patent application Ser. No. 12/047,249, now U.S. Pat. No.7,852,017, entitled “Ballast for Light Emitting Diode Light Sources,”inventor John L. Melanson, and filed on Mar. 12, 2008 describesexemplary methods and systems and is incorporated by reference in itsentirety.

U.S. patent application Ser. No. 11/926,864, entitled “Color Variationsin a Dimmable Lighting Device with Stable Color Temperature LightSources,” inventor John L. Melanson, and filed on Mar. 31, 2007describes exemplary methods and systems and is incorporated by referencein its entirety. Referred to herein as Melanson I.

U.S. Provisional Application No. 60/909,457, entitled “Multi-FunctionDuty Cycle Modifier,” inventors John L. Melanson and John Paulos, andfiled on Mar. 31, 2007 describes exemplary methods and systems and isincorporated by reference in its entirety. Referred to herein asMelanson II.

U.S. patent application Ser. No. 12/047,258, now U.S. Pat. No.8,018,171, entitled “Multi-Function Duty Cycle Modifier,” inventors JohnL. Melanson and John Paulos, and filed on Mar. 12, 2008 describesexemplary methods and systems and is incorporated by reference in itsentirety. Referred to herein as Melanson III.

U.S. patent application Ser. No. 11/695,024, entitled “Lighting Systemwith Lighting Dimmer Output Mapping,” inventors John L. Melanson andJohn Paulos, and filed on Mar. 31, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety.

U.S. patent application Ser. No. 11/864,366, entitled “Time-BasedControl of a System having Integration Response,” inventor John L.Melanson, and filed on Sep. 28, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety. Referred toherein as Melanson IV.

U.S. patent application Ser. No. 11/967,269, entitled “Power ControlSystem Using a Nonlinear Delta-Sigma Modulator with Nonlinear PowerConversion Process Modeling,” inventor John L. Melanson, and filed onDec. 31, 2007 describes exemplary methods and systems and isincorporated by reference in its entirety. Referred to herein asMelanson V.

U.S. patent application Ser. No. 11/967,275, entitled “ProgrammablePower Control System,” inventor John L. Melanson, and filed on Dec. 31,2007 describes exemplary methods and systems and is incorporated byreference in its entirety. Referred to herein as Melanson VI.

U.S. patent application Ser. No. 12/047,262, now U.S. Pat. No.7,804,256, entitled “Power Control System for Voltage Regulated LightSources,” inventor John L. Melanson, and filed on Mar. 12, 2008describes exemplary methods and systems and is incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates in general to the field of electronics andlighting, and more specifically to a system and method to determinepower factor correction control parameters from phase delays in a phasemodulated signal.

Description of the Related Art

Commercially practical incandescent light bulbs have been available forover 100 years. However, other light sources show promise ascommercially viable alternatives to the incandescent light bulb. LEDsare becoming particularly attractive as main stream light sources inpart because of energy savings through high efficiency light output andenvironmental incentives such as the reduction of mercury.

LEDs are semiconductor devices and are driven by direct current. Thelumen output intensity (i.e. brightness) of the LED approximately variesin direct proportion to the current flowing through the LED. Thus,increasing current supplied to an LED increases the intensity of the LEDand decreasing current supplied to the LED dims the LED. Current can bemodified by either directly reducing the direct current level to thewhite LEDs or by reducing the average current through duty cyclemodulation.

Dimming a light source saves energy when operating a light source andalso allows a user to adjust the intensity of the light source to adesired level. Many facilities, such as homes and buildings, includelight source dimming circuits (referred to herein as “dimmers”).

FIG. 1 depicts a lighting system 100 that generates a link voltageV_(LINK) and a drive current i_(OUT) to illuminate the light source 102.An alternating current (AC) voltage source 101 such as a power plantgenerates a mains voltage V_(mains), which provides power for lightingsystem 100. The particular frequency and root mean square (RMS) value ofmains voltage V_(mains) is generally location specific and is nominally60 Hz/120 VAC in the United States and 50 Hz/230 VAC in Europe andelsewhere. The lighting system 100 includes a dimmer 104 to generate araw phase modulated signal V_(Φ) _(_) _(RAW). Rectifier 105 rectifiesthe raw phase modulated signal V_(Φ) _(_) _(RAW) to generate a rectifiedphase modulated signal V_(Φ). Rectifier 105 is, for example, afull-bridge diode rectifier. The phase delay of each cycle of the phasemodulated signal V_(Φ) indicates a particular dimming level. Dimmer 104can be any conventional dimmer that generates a phase modulated signal,such as a triac based dimmer as described in Melanson I.

The lighting system 100 also includes a light source driver circuit 106to receive the phase modulated signal V_(Φ). In at least one embodiment,light source driver circuit 106 is a switching power converter with aninternal PFC switch (not shown) that controls power factor correctionand boosting phase modulated signal V_(Φ) to the link voltage V_(LINK).The light source driver circuit 106 modulates the light source drivecurrent i_(OUT) in response to the dimming level indicated by phasemodulated signal V_(Φ). The light source driver circuit 106 modulatesthe light source drive current i_(OUT) by turning the light source drivecurrent i_(OUT) “on” and “off” to achieve an average value of lightsource drive current i_(OUT) corresponding to the dimming levelindicated by phase modulated signal V_(Φ). The drive current i_(OUT)causes the light source 102 to illuminate, and modulating the drivecurrent i_(OUT) varies the brightness of light source 102. Thus, lightsource driver circuit 106 attempts to modulate the drive current i_(OUT)so that light source 102 dims to a level indicated by phase modulatedsignal V_(Φ).

For an LED based light source 102, the link voltage V_(LINK) can be 400V or more. To dim light source 102, light source driver circuit 106decreases the duty cycle of control signal C_(s) and, thus, decreasesthe drive current i_(OUT). When dimmed, the power demand of light source102 decreases. When the power demand of light source 102 decreases,light source driver circuit 106 decreases the duty cycle of the internalswitch (not shown) that controls the voltage boost of phase modulatedsignal V_(Φ) to link voltage V_(LINK). Despite decreasing power demand,light source driver circuit 106 maintains the link voltage V_(LINK) atan approximately constant level. The switching efficiency of lightsource driver circuit 106 steadily decreases as 106 continues to boostthe link voltage V_(LINK) to a voltage used during full power demand bylight source 102 despite the lower power demands of a dimmed lightsource 102. The efficiency loss becomes more prominent, for example,when a duty cycle of the internal PFC switch of light source drivercircuit 106 is less than 50%.

Decreasing power demand by light source 102 when dimming light source102 can actually increase power demand by light source driver circuit106. Light source driver circuit 106 attempts to provide unity powerfactor correction so that the light source driver circuit 106 appearsresistive to the AC voltage source 101. Thus, looking into terminals Aand B, ideally light source driver circuit 106 has an effectiveresistance R_(EFF) _(_) ₀ as perceived by the AC voltage source 101. Thevalue of the effective resistance R_(EFF) _(_) ₀ equals V_(Φ)/i_(IN),where V_(Φ) is a phase modulated signal and i_(IN) is the input currentinto light source driver circuit 106. As the power demand by lightsource 102 decreases when dimmed, the current i_(IN) actually increases,thus, decreasing the effective resistance R_(EFF) _(_) ₀, thus, drawingmore power from AC voltage source 101. Decreasing the effectiveresistance R_(EFF) _(_) ₀ of light source driver circuit 106 whendimming light source 102 represents an inefficient use of power.

FIG. 2A depicts a series of voltage waveforms 200 that represent tworespective cycles of waveforms present in lighting system 100. Supplyvoltage V_(mains) is a sine wave depicted with two exemplary cycles 202and 204. Dimmer 104 generates a raw phase modulated signal V_(Φ) bychopping each half cycle of supply voltage V_(mains) to generateidentical leading edge phase delay α1 for each respective half cycle ofcycle 206. The phase delays of the raw phase modulated signal V_(Φ)increase as the dimming level decreases, i.e. the brightness of lightsource 102 decreases. Half cycle 208 indicates longer phase delays α2corresponding to a decrease in dimming level. The leading edge phasedelays αX represent the elapsed time between a beginning of a half cycleand a leading edge of the phase modulated mains voltage V_(Φ), where Xis an index value. The rectified cycles 210 and 212 of phase modulatedsignal V_(Φ) have the same respective phase delays α1 and α2 as the rawphase modulated signal V_(Φ RAW).

Conventional dimmers, such as a triac based dimmer, that are designedfor use with inactive loads, such as incandescent light bulbs, often donot perform well when supplying a raw phase modulated signal V_(Φ) _(_)_(RAW) to an active load such as light source driver circuit 106. Forexample, when supplying an active load, the dimmer can miss generatingphase delays in some cycles of raw phase modulated signal V_(Φ) _(_)_(RAW) and can generate ripple during the phase delays. Exemplaryproblems with at least one conventional dimmer when used with an activeload are described in Rand et al., “Issues, Models and Solutions forTriac Modulated Phase Dimming of LED Lamps”, June, 2007, pages 1398-1404of Power Electronics Specialists Conference, 2007. PESC 2007, publishedby the Institute of Electrical and Electronic Engineers, ISBN978-1-4244-0655-5.

FIG. 2B depicts an LED driver circuit 250 available from Supertex, Inc.of Sunnyvale, Calif., USA. LED driver circuit 250, represents oneembodiment of light source driver circuit 106. The LED driver circuit250 is described in more detail in Supertex design note DN-H05 availablefrom Supertex, Inc. The LED driver circuit 250 includes two extracircuits, damper circuit 252 and bleeder circuit 254 to providecompatibility with a dimmer, such as dimmer 104. According to DN-H05,the damper circuit 252 provides damped charging of the driver's inputfilter circuit at P16. The damper circuit 252 provides resistive dampingto prevent AC line input current oscillations due to a sudden rise of anAC line voltage, such as the edges of phase modulated signal V_(Φ). Thebleeder circuit 254 provides a nominal 1 kohm load to a rectified ACline at P21 to suppress a voltage rise at the input capacitors C21-C23during phase delays of phase modulated signal V_(Φ) which couldotherwise cause flicker of a lamp driven by LED driver circuit 250.

FIG. 2C depicts a unity power factor LED lamp driver 280, whichrepresents one embodiment of light source driver circuit 106. The LEDlamp driver 280 is described in more detail with reference to FIG. 9 inSupertex application note AN-H52 available from Supertex, Inc. LED lampdriver 280 includes damping circuitry 282 to add a load to dimmer 104during phase delays of phase modulated signal. The damping circuitry 282includes a bleeder resistor R_(BL) that is connected by transistor M2during phase delays of a phase modulated input signal to lamp driver280. When transistor M2 conducts, the bleeder resistor R_(BL) providesan added load to the AC line at V_(IN) to dampen the phase modulatedsignal during phase delays. Adding an extra transistor M2 and resistorR_(BL) increases the system cost of lamp driver 280.

The light source driver circuit 106 exhibits one or more inefficiencieswhen dimming light source 102. For example, when the power demand bylight source 102 decreases, the link voltage remains approximatelyconstant. Additionally, when power demand by light source 102 decreases,the effective resistance R_(EFF) _(_) ₀ of light source driver circuit106 increases, thus drawing more power from AC voltage source 101despite the lower power demands by light source 102. Additionally, addedcircuitry to conventional LED driver circuits adds cost to the LEDdriver circuits.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a light emitting diode (LED)lighting system includes a power factor correction (PFC) controller. Thecontroller includes an input to receive a phase delay signal indicatinga phase delay of a phase modulated dimmer signal. The controller alsoincludes a digital signal processor, coupled to the input, to receivethe phase delay signal and determine a PFC control operating parameterfrom the phase delay signal and to generate a PFC switch control signalusing the determined operating parameter.

In another embodiment of the present invention, a method of controllinga light emitting diode (LED) lighting system includes receiving a phasedelay signal indicating a phase delay of a phase modulated dimmersignal, determining a PFC control operating parameter from the phasedelay signal using a digital signal processor, and generating a PFCswitch control signal using the determined operating parameter.

In a further embodiment of the present invention, a light emitting diode(LED) lighting system includes a power factor correction (PFC)controller to receive a signal indicating a dimming level and togenerate a PFC switch control signal to cause a PFC LED driver circuitto respond to the dimming level indicated by the signal withoutdecreasing an effective resistance of the PFC load driver circuit, asperceived by a voltage source of the PFC load driver circuit, as thedimming level indicated by the signal increases.

In a further embodiment of the present invention, a method ofcontrolling a light emitting diode (LED) lighting system includesreceiving a signal indicating a dimming level and generating a powerfactor correction control signal to cause a PFC LED driver circuit torespond to the dimming level indicated by the signal without decreasingan effective resistance of the PFC load driver circuit, as perceived bya voltage source of the PFC load driver circuit, as the dimming levelindicated by the signal increases.

In a further embodiment of the present invention, a light emitting diode(LED) lighting system includes a power factor correction (PFC)controller to generate a duty cycle modulated control signal to controla regulated link voltage of a PFC LED driver circuit and to decrease thelink voltage when a duty cycle of the control signal decreases to avalue between zero and a duty cycle threshold value.

In a further embodiment of the present invention, a method ofcontrolling a light emitting diode (LED) lighting system includesgenerating a duty cycle modulated control signal to control a regulatedlink voltage of a PFC LED driver circuit; and decreasing the linkvoltage when a duty cycle of the control signal decreases to a valuebetween zero and a duty cycle threshold value.

In a further embodiment of the present invention, a light emitting diode(LED) lighting system includes a power factor correction (PFC)controller includes: an input to receive a phase delay signal indicatinga phase delay of a phase modulated dimmer signal. The PFC controller isconfigured to receive the phase delay signal and to generate pulses forthe PFC switch control signal during the phase delays of the phasemodulated signal. The pulse widths and duty cycles of the pulses of thePFC switch control signal generated during the phase delays arcsufficient to attenuate ripple of the phase modulated signal during thephase delays of phase modulated signal.

In a further embodiment of the present invention, a method ofcontrolling a light emitting diode (LED) lighting system includesreceiving a phase delay signal indicating a phase delay of a phasemodulated dimmer signal and generating pulses for a PFC switch controlsignal during the phase delays of the phase modulated signal. The pulsewidths and duty cycles of the pulses of the PFC switch control signalgenerated during the phase delays are sufficient to attenuate ripple ofthe phase modulated signal during the phase delays of phase modulatedsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features and advantages made apparent to those skilled in theart by referencing the accompanying drawings. The use of the samereference number throughout the several figures designates a like orsimilar element.

FIG. 1 (labeled prior art) depicts a lighting system with a power factorcorrection driver circuit and controller.

FIG. 2A (labeled prior art) depicts various waveforms present in thelighting system of FIG. 1.

FIG. 2B (labeled prior art) depicts an LED driver circuit with dimmerswitch compatibility circuits.

FIG. 2C (labeled prior art) depicts another LED driver circuit withdimmer switch compatibility circuitry.

FIG. 3 depicts a light emitting diode lighting system with a powerfactor correction controller that derives one or more power factorcorrection control parameters from a phase modulated signal.

FIGS. 4 and 5 depict phase modulated signals having various leading andtrailing edge phase delays.

FIG. 6 depicts a phase delay detector.

FIG. 7 depicts exemplary phase modulated signal and associated PFCswitch control signal waveforms.

FIG. 8 depicts an effective resistance model of a PFC LED drivercircuit.

FIG. 9 depicts relationships between a phase modulated signal and aninductor current with and without dimming.

FIG. 10 depicts a relationship between duty cycles of a PFC switchcontrol signal and a link voltage.

FIGS. 11 and 12 depict LED apparatuses.

DETAILED DESCRIPTION

A light emitting diode (LED) lighting system includes a power factorcorrection (PFC) controller that determines at least one power factorcorrection control parameter from phase delays of a phase modulatedsignal. In at least one embodiment, a peak voltage of the phasemodulated signal is a PFC control parameter used by the PFC controllerto control power factor correction and generation of a link voltage by aPFC LED driver circuit. The phase delays are related to a peak voltageof the phase modulated signal. Thus, in at least one embodiment,detecting the phase delay in one or more cycles of the phase modulatedsignal allows the PFC controller to determine the peak voltage of thephase modulated signal.

The PFC LED driver circuit supplies an output current to drive LED(s) ofan LED apparatus. As the dimming level decreases, the PFC controllerdecreases a duty cycle of a PFC switch in the PFC LED driver circuit tocause the PFC LED driver circuit to decrease the output current suppliedto the LEDs. When the phase modulated signal indicates a dimming levelbelow a threshold value, the PFC controller maintains an approximatelyconstant duty cycle of the PFC switch to, for example, maintainswitching efficiency without significantly sacrificing power factorcorrection.

In at least one embodiment, PFC controller generates a PFC switchcontrol signal to cause the PFC LED driver circuit to respond todecreasing dimming levels as indicated by a dimming signal, such as thephase modulated signal, without decreasing an effective resistance ofthe PFC LED driver circuit, as perceived by a voltage source of the PFCLED driver circuit, as the dimming level indicated by the dimming signalincreases. The phase modulated signal represents one embodiment of thedimming signal.

In at least one embodiment, the PFC controller generates a duty cyclemodulated control signal to control a regulated link voltage of the PFCLED driver circuit and decreases the link voltage when a duty cycle ofthe control signal decreases to a value between zero and a duty cyclethreshold value.

In at least one embodiment, the PFC controller generates approximatelyconstant pulse widths for the PFC switch control signal during eachcycle of phase modulated signal when a duty cycle of PFC switch controlsignal is below a predetermined threshold.

In at least one embodiment, the PFC controller generates pulses for thePFC switch control signal during the phase delays of phase modulatedsignal, wherein the pulses of PFC switch control signal generated duringthe phase delays have a period significantly greater than a period ofthe pulses of PFC switch control signal during an active period of phasemodulated signal.

FIG. 3 depicts a lighting system 300 having a PFC controller 302 and aPFC LED driver circuit 304. The PFC controller 302 generates a dutycycle modulated PFC switch control signal CS₁ to control theconductivity of switch 306. Switch 306 can be any switch, and, in atleast one embodiment, switch 306 is an n-channel field effect transistor(FET). The PFC LED driver circuit 304 is a switching power converterthat boosts the phase modulated signal V_(Φ) to a link voltage V_(C1)across hold-up capacitor 308. In at least one embodiment, the linkvoltage V_(C1) has a peak voltage in the range of 200V-400 V. Whenswitch 306 is “OFF” (i.e. non-conductive), diode 310 is forward biased,and inductor 312 drives inductor current i_(L1) through diode 310. Theinductor current i_(L1) through diode 310 charges capacitor 308 tomaintain an approximately constant link voltage V_(C1). When switch 306is “ON” (i.e. conductive), the voltage across inductor 312 reverses,diode 310 is reverse biased, and the inductor 312 energizes with thecurrent i_(L1). PFC controller 302 controls the duty cycles of PFCswitch control signal CS₁ and switch 306 so that current i_(L1) isproportional to phase modulated signal V_(Φ). Capacitor 314 providesfiltering to smooth drive current i_(L1) so that the average drivecurrent i_(L1) is sinusoidal and in phase with phase modulated signalV_(Φ).

The PFC controller 302 includes a digital signal processor 316 toperform various operations including determining the pulse width andduty cycle of PFC switch control signal CS₁. Digital signal processor316 is, for example, a digital signal processor. In at least oneembodiment, the PFC controller 302 determines the pulse width and dutycycle of PFC switch control signal CS₁ utilizing the algorithmsdisclosed in Melanson V and Melanson VI.

In at least one embodiment, the pulse width T1 of PFC switch controlsignal CS₁ is determined by digital signal processor 316 by executing acontrol signal state algorithm represented by Equation [1]:

$\begin{matrix}{{T\; 1^{2}} = {\frac{2 \cdot L}{V_{{\Phi\_{pk}}^{2}}} \cdot P \cdot {TT} \cdot {\left( {1 - \frac{V_{\Phi}}{V_{C\; 1}}} \right).}}} & \lbrack 1\rbrack\end{matrix}$“T1” is the pulse width of the PFC switch control signal CS₁. “L”represents an inductance value of inductor 312. “V_(Φ) _(_) _(pk)” is apeak voltage of phase modulated signal V_(Φ) without phase delays. “P”represents a power demand variable related to the power demand of LEDapparatus 322. In at least one embodiment, P is a proportionalintegrator output value as described in Melanson V and Melanson VI. “TT”is the period of PFC switch control signal CS₁ and, in at least oneembodiment, is also determined as described in Melanson V and MelansonVI. “V_(Φ)” is a sampled value of phase modulated signal V_(Φ). “V_(C1)”is a sampled value of the link voltage V_(C1).

In at least one embodiment, all of the PFC control parameters ofEquation [1] are known, can be reliably determined directly, or can bereliably determined from the feedback signals V_(Φ)′ and V_(C1)′ exceptV_(Φ) _(_) _(pk). Because phase modulated signal V_(Φ) includes phasedelays when dimming the LEDs of LED apparatus 322, the peak voltageV_(Φ) _(_) _(pk) of phase modulated signal V_(Φ) cannot always bedirectly measured. However, as described in conjunction with FIGS. 4 and5, the phase delays of phase modulated signal V_(Φ) can be used bydigital signal processor 316 to estimate V_(Φ) _(_) _(pk).

In at least one embodiment, PFC controller 302 also controls the outputcurrent i_(OUT) in accordance with the exemplary systems and methodsdescribed in Melanson IV.

FIGS. 4 and 5 depict cycles of phase modulated signal V_(Φ) havingvarious leading and trailing edge phase delays. Waveforms 400 representtwo cycles 402 and 404 having a peak voltage of V_(Φ) _(_) _(pk). Cycle402 includes two phase delays α0 and α1, and cycle 404 includes twophase delays α2 and α3. The peak voltage V_(Φ) _(_) _(pk) can bemeasured directly from cycle 402 because the phase delays α0 and α1 areless than T/4, where T is the period of phase modulated signal V_(Φ).However, the peak voltage V_(Φ) _(_) _(pk) cannot be measured directlyfrom cycle 404 because the phase delays α2 and α3 are greater than T/4.Although the peak voltage V_(Φ) _(_) _(pk) can be measured directly fromcycle 402, in at least one embodiment, the digital signal processor 316determines the peak voltage V_(Φ) _(_) _(pk) for all cycles of phasemodulated signal V_(Φ). In at least one embodiment, the digital signalprocessor 316 periodically or intermittently determines the peak voltageV_(Φ) _(_) _(pk). In at least one embodiment, the digital signalprocessor 316 measures each peak voltage V_(Φ) _(_) _(pk) from eachcycle that can be measured.

Referring to FIGS. 3, 4, and 5, phase delay detector 318 receives phasemodulated signal V_(Φ) and, in at least one embodiment, determines adigital value of each phase delay αX and βX in each cycle of phasemodulated signal V_(Φ), where X is an index value. To determine the peakvoltage V_(Φ) _(_) _(pk) from the phase delays of phase modulated signalV_(Φ), phase delay detector 318 detects the phase delays of each cycleof phase modulated signal V_(Φ). In at least one embodiment, phase delaydetector 318 generates a digital value of phase delay signal Φ for eachphase delay detected in phase modulated signal V_(Φ). Each digital valueof phase delay signal Φ represents a phase delay, and each phase delayindicates a dimming level. For example, a 50 Hz phase modulated signalV_(Φ) has a period of 1/50 or 0.02 seconds. A dimming level of 25% isrepresented by a phase delay of (0.5·0.02)·0.25 seconds. Where(0.5·0.02) represents the duration of each half cycle of phase modulatedsignal V_(Φ) and 0.25 represents the dimming level. Thus, each phasedelay signal Φ can also be referred to as a dimmer signal.

Digital signal processor 316 determines the peak voltage V_(Φ) _(_)_(pk) from the phase delay signal Φ. Each half cycle of phase modulatedsignal V_(Φ) represents 180 degrees. Each phase delay can be convertedinto an equivalent phase angle in accordance with Equation [2]:phase angle=(2·phase delay)/(T)×180°  [2]where T is the period of phase modulated signal V_(Φ).

In at least one embodiment, digital signal processor 316 determines thepeak voltage V_(Φ) _(_) _(pk) in accordance with Equation [3]:V _(Φ) _(_) _(pk)=abs{V _(Ax)/[sin(phase angle)]}  [3],where “abs” represents the absolute value function of the quantityenclosed by the brackets and V_(Ax) represents a peak voltage of theleading or trailing edge associated with the phase delay, and “x” is anindex.

For example, if phase modulated signal V_(Φ) is a 50 Hz signal andα0=α1, from Equations [2] and [3] the peak voltage V_(Φ) _(_) _(pk) forthe first half of cycle 402 equals abs{V_(A0)/[sin((2·α0)/0.02)·180)].If α2=α3, from Equations [2] and [3], the peak voltage V_(Φ) _(_) _(pk)for the second half of cycle 402 equalsabs{V_(A1)/[sin((2·α2)/0.02)·180)].

In at least one embodiment, phase delays α0 and α1 are independentlygenerated as, for example, described in Melanson H and Melanson III.When phase delays in a cycle are independently generated, the peakvoltage V_(Φ) _(_) _(pk) can be updated for each independently generatedphase delay.

FIG. 5 depicts a leading edge phase delay α0 and a trailing edge phasedelay β0. In at least one embodiment, digital signal processor 316determines the peak voltage V_(Φ) _(_) _(pk) in accordance withEquations [2] and [3] for independently generated leading and trailingedge phase delays. When detecting independently generated leading andtrailing edge phase delays, in at least one embodiment, digital signalprocessor 316 receives the raw phase modulated signal V_(Φ) _(_) _(RAW)to determine start and stop times of each half cycle of a cycle by, forexample, sensing the polarity of each half cycle.

FIG. 6 depicts a time-based phase delay detector 600 that represents oneembodiment of phase delay detector 318. Comparator 602 compares phasemodulated signal V_(Φ) to a known reference Vref. The reference V_(ref)is generally the cycle cross-over point voltage of phase modulatedsignal V_(Φ), such as a neutral potential of a building AC voltage. Inat least one embodiment, the reference V_(ref) is a voltage value justgreater than any expected voltage ripples of the neutral potential. Thecounter 604 counts the number of cycles of clock signal f_(clk) thatoccur until the comparator 602 indicates that an edge of phase modulatedsignal V_(Φ) has been reached. Since the frequency of phase modulatedsignal V_(Φ) and the frequency of clock signal f_(clk) is known, thephase delay indicated by phase delay signal Φ can be determined from thecount of cycles of clock signal f_(clk) that occur until the comparator602 indicates that the edge of phase modulated signal V_(Φ) has beenreached. Thus, phase delay detector 600 is a time-based phase delaydetector that detects the phase delays phase delay indicated by phasedelay signal Φ using a time-based process.

FIG. 7 depicts exemplary waveforms 700 representing one cycle 702 ofphase modulated signal V_(Φ) and pulse waveforms of PFC switch controlsignal CS₁. In at least one embodiment, the PFC controller 302 continuesto pulse the PFC switch 306, i.e. turn the PFC switch 306 ON and OFF,during phase delays of phase modulated signal V_(Φ) to increase theeffective resistance R_(EFF) _(_) ₁ of PFC LED driver circuit 304without additional external components and without additional loss ofefficiency.

The phase delays α2 of cycle 702 of phase modulated signal V_(Φ)indicate dimming levels for the LEDs. Increasing phase delays indicateincreasing dimming levels and decreasing power demand from PFC LEDdriver circuit. Referring to FIGS. 3 and 7, half cycles 704 and 706 ofphase modulated signal V_(Φ) each include respective active (uncut)regions 708 and 710 having an active time period T_(A) (referred to as“active period T_(A)”). The active period T_(A) plus the phase delay α2equals the half cycle period T/2 of cycle 702. Referring to FIG. 1,conventional PFC driver circuit and controllers, such as light sourcedriver circuit 106, cut off the output current i_(OUT) during the phasedelay α2. The phase modulated signal V_(Φ) of FIG. 1 often has ripplesduring the phase delay α2 that can cause problems, such as making theedges of phase modulated signal V_(Φ) difficult to detect.

Referring to FIGS. 3 and 7, in at least one embodiment, during the phasedelay α2, PFC controller 302 generates pulses 712 that decrease theeffective resistance R_(EFF) _(_) ₁ of PFC switch control signal CS₁ andattenuates ripples of phase modulated signal V_(Φ) during phase delayα2. By attenuating the ripples of phase modulated signal V_(Φ) duringα2, phase modulated signal V_(Φ) is approximately 0 V during phase delayα2 as shown in cycle 702. Attenuating the ripples facilitates moreaccurate edge detection by phase delay detector 318. A more accurateedge detection facilitates a more accurate determination of the dimminglevel indicated by phase modulated signal V_(Φ) and a more accuratedetermination of peak voltage V_(Φ) _(_) _(pk). The periods and dutycycles of PFC switch control signal CS₁ during phase delay α2 are notdrawn to scale. In at least one embodiment, the periods and duty cyclesof PFC switch control signal CS₁ are sufficient enough to attenuate theripples of phase modulated signal V_(Φ). In at least one embodiment, theperiod of PFC switch control signal CS₁ during phase delay α2 is 0.0001seconds to 0.0002 seconds, which equates to a switching frequencyranging from 10 kHz to 20 kHz. Keeping a dimmer, such as dimmer 104(FIG. 1) loaded during phase delays improves dimmer performance, thus,removing the need for the additional damping circuitry 282 of LED lampdriver 280 (FIG. 2).

Generally, during the active period T_(A) of phase modulated signalV_(Φ), PFC controller 302 determines the pulse widths of PFC switchcontrol signal CS₁ in accordance with Equation [1]. However, as thephase delay α2 increases, the duty cycle of PFC switch control signalCS₁ also decreases. In at least one embodiment, once the duty cycle ofPFC switch control signal CS₁ is below a duty cycle threshold, the[1−(V_(Φ)/V_(C1))] term of Equation [1] becomes approximately 1.Accordingly, in at least one embodiment, once the duty cycle of PFCcontroller 302 is below the duty cycle threshold, PFC controller 302generates pulses 714 of PFC switch control signal CS₁ with a constantpulse width and constant duty cycle. In at least one embodiment, the PFCcontroller 302 generates pulses 714 within a frequency range of 25 kHzto 150 kHz to avoid audio frequencies at the low frequency end and avoidswitching inefficiencies on the high frequency end. Additionally, inlighting applications, frequencies associated with commercial electronicdevices, such as infrared remote controls, are avoided. In at least oneembodiment, the particular duty cycle threshold is a matter of designchoice and is, for example, chosen to be a duty cycle when[1−(V_(Φ)/V_(C1))] term of Equation [1] becomes approximately 1 so thatthe decreasing the duty cycle does not have an unacceptable effect onthe performance of lighting system 300. In at least one embodiment, theduty cycle threshold is 0.4.

Pulses 716 of control signal CS₁ represent a time expanded window 718 ofpulses 714 to illustrate the constant pulse widths of pulses 714. Thepulses 716 are exemplary and not necessarily to scale. The duration ofwindow 718 is T_(A)/X, and X is a factor equal to 5/(frequency of PFCswitch control signal CS₁).

FIG. 8 depicts an effective resistance model of PFC LED driver circuit304. PFC LED driver circuit 304 has an effective resistance R_(EFF) _(_)₁ from the perspective of a mains voltage source such as the AC voltagesource 101 (FIG. 1). In at least one embodiment, PFC controller 302generates a PFC switch control signal CS₁ to cause PFC LED drivercircuit 304 to respond to the dimming level indicated by the phase delaysignal Φ without decreasing an effective resistance R_(EFF) _(_) ₁ ofthe PFC LED driver circuit 304, as perceived by a voltage source of thePFC LED driver circuit 304, as the dimming level indicated by the signalincreases. Keeping the effective resistance R_(EFF) _(_) ₁ of the PFCLED driver circuit 304 from decreasing as dimming levels increaseconserves power.

In at least one embodiment, digital signal processor 316 monitors powerdemand of the LED apparatus 322 by monitoring the value of power demandvariable P in Equation [1]. As power demand of the LED apparatus 322decreases due to, for example, increased dimming, the value of powerdemand variable P decreases. By determining the pulse width of PFCswitch control signal CS₁ in accordance with Equation [1], digitalsignal processor 316 decreases the pulse width and, thus, the duty cycleof PFC switch control signal CS₁. Decreasing the duty cycle of PFCswitch control signal CS₁ keeps the effective resistance R_(EFF) _(_) ₁from increasing with increasing dimming levels.

FIG. 9 depicts exemplary relationships between phase modulated signalV_(Φ) and the inductor current i_(L1) without dimming in view 902 andwith dimming in view 904. Referring to FIGS. 3 and 9, the effectiveresistance R_(EFF) _(_) ₁ of PFC load driver circuit 304 equalsV_(Φ)/i_(L1). In view 902, phase modulated signal V_(Φ) has no phasedelays, which indicates no dimming. Because PFC load driver circuit 304is power factor corrected, the inductor current i_(L1) tracks and is inphase with the phase modulated signal V_(Φ). In view 904, phasemodulated signal V_(Φ) includes phase delays α1 and α2, which indicatesdimming. The dashed lined waveforms 906 and 908 represent the values ofthe inductor current i_(L1) if the inductor current i_(L1) had notdecreased with dimming. The solid lined waveforms 910 and 912 indicatethe actual value of inductor current i_(L1) as controlled by PFCcontroller 302. Thus, the effective resistance R_(EFF) _(_) ₁ of PFCload driver circuit 304 does not decrease as dimming levels increaseand, in at least one embodiment actually increases as dimming levelsincrease.

FIG. 10 depicts an exemplary, graphical relationship 1000 between dutycycles of PFC switch control signal CS₁ and the link voltage V_(C1).Referring to FIGS. 3 and 10, PFC load driver circuit 304 boosts thephase modulated signal V_(Φ) to different link voltages V_(C1) dependingupon the duty cycle of PFC switch control signal CS₁. Decreasing thepower demand of LED apparatus 322 results in a decreasing value of thepower demand variable P in Equation [1]. In accordance with Equation[1], PFC controller 302 responds to decreasing power demand by LEDapparatus 322 by decreasing the duty cycle of PFC switch control signalCS₁. The decreasing power demand by LED apparatus 322 is, for example,caused by dimming the LEDs of LED apparatus 322. In at least oneembodiment, boosting the phase modulated signal V_(Φ) to the high linkvoltage V_(C1) _(_) _(H) results in a boost of 120 VAC to anapproximately 400 V direct current voltage. As the duty cycle of PFCswitch control signal CS₁ decreases with decreased power demand by LEDapparatus 322, PFC load driver circuit 304 loses efficiency via, forexample, switching losses associated with switch 306.

Accordingly, in at least one embodiment, PFC controller 302 generatesthe duty cycle modulated PFC switch control signal CS₁ to control theregulated link voltage V_(C1) of the PFC LED driver circuit 304. PFCcontroller 302 decreases the link voltage V_(C1) from a high linkvoltage value V_(C1) _(_) _(H) to a low link voltage value V_(C1) _(_)_(L) when the duty cycle of the PFC switch control signal CS₁ decreasesto a value between zero and a duty cycle threshold DC_(TH). Theparticular value of the duty cycle threshold DC_(TH) is a matter ofdesign choice and is, for example, chosen to increase the efficiency ofPFC load driver circuit 304 while providing an adequate link voltageV_(C1) to provide the power demand needs of LED apparatus 322. In atleast one embodiment, the duty cycle threshold DC_(TH) is set at 0.5. Inat least one embodiment, for phase modulated signal V_(Φ) having avoltage peak V_(Φ) _(_) _(pk) of 120V, the high link voltage V_(C1) _(_)_(H) is any value within a range of approximately 200V to 400V for a lowlink voltage W_(C1) _(_) _(L) having a respective value within a rangeof approximately 120V to 175V.

The slope and shape of the transition 1002 from the high link voltageV_(C1) _(_) _(H) to the low link voltage are matters of design choiceand depend upon, for example, a desired transition between high linkvoltage V_(C1) _(_) _(H) and the low link voltage V_(C1) _(_) _(L). Inat least one embodiment, the slope is 90 degrees, which indicates twopossible values, V_(C1) _(_) _(H) and V_(C1) _(_) _(L), for link voltageV_(C1). In other embodiments, the slope is less than 90 degrees andindicates multiple values of link voltage V_(C1) between high linkvoltage V_(C1) _(_) _(H) and the low link voltage V_(C1) _(_) _(L). Theshape of transition 1002 can be linear or nonlinear.

FIGS. 11 and 12 depict exemplary embodiments of LED apparatus 322. LEDapparatus 1100 includes one or more LED(s) 1102. The LED(s) 1102 can beany type of LED including white, amber, other colors, or any combinationof LED colors. Additionally, the LED(s) 1102 can be configured into anytype of physical arrangement, such as linearly, circular, spiral, or anyother physical arrangement. In at least one embodiment, each of LED(s)1102 is serially connected. Capacitor 1104 is connected in parallel withLED(s) 1102 and provides filtering to protect the LED(s) 1102 from ACsignals. Inductor 1106 smoothes energy from LED current i_(OUT) tomaintain an approximately constant current i_(OUT) when PFC switch 306is ON. Diode 1108 allows continuing current flow when switch PFC 306 isOFF.

In switching LED system 1210, inductor 1212 is connected in series withLED(s) 1102 to provide energy storage and filtering. Inductor 1212smoothes energy from LED current i_(OUT) to maintain an approximatelyconstant current i_(OUT) when PFC switch 306 is ON. Diode 1214 allowscontinuing current flow when PFC switch 306 is OFF. Although twospecific embodiments of LED apparatus 322 have been described, LEDapparatus 322 can be any LED, array of LED(s), or any switching LEDsystem.

Thus, a PFC controller 302 determines at least one power factorcorrection control parameter from phase delays of phase modulated signalV_(Φ).

In at least one embodiment, as a dimming level decreases, the PFCcontroller 302 decreases a duty cycle of PFC switch 306 in the PFC LEDdriver circuit 304 to cause the PFC LED driver circuit 304 to decreasethe output current supplied to the LEDs. When the phase modulated signalV_(Φ) indicates a dimming level below a threshold value Φ_(TH), the PFCcontroller 302 maintains an approximately constant duty cycle of the PFCswitch 306 to, for example, maintain switching efficiency withoutsignificantly sacrificing power factor correction.

In at least one embodiment, PFC controller 302 generates a PFC switchcontrol signal CS₂ to cause the PFC LED driver circuit 304 to respond todecreasing dimming levels as indicated by a dimming signal, such as thephase modulated signal V_(Φ), without decreasing an effective resistanceof the PFC LED driver circuit 304.

In at least one embodiment, the PFC controller 302 generates a dutycycle modulated PFC switch control signal CS₁ to control a regulatedlink voltage V_(C1) of the PFC LED driver circuit 304 and decreases thelink voltage V_(C1) when a duty cycle of the PFC switch control signalCS₁ decreases to a value between zero and a duty cycle threshold valueDC_(TH).

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. A light emitting diode (LED) lighting systemcomprising: a controller comprising: an input to receive a phase delaysignal indicating a phase delay of a phase modulated dimmer signal; anda signal processor, coupled to the input, to receive the phase delaysignal and determine a control operating parameter from the phase delaysignal and to generate a switch control signal using the determinedoperating parameter to vary an input current to a switching powerconverter with a phase modulated voltage and to maintain a regulatedlink voltage at an approximately constant value until a duty cycle ofthe control signal decreases to a predetermined threshold value and todecrease the regulated link voltage of the switching power converterwhen the duty cycle of the control signal decreases to the predeterminedduty cycle threshold value.
 2. The LED lighting system of claim 1further comprising: the switching power converter coupled to thecontroller; and a load coupled to the switching power converter, whereinthe load includes one or more light emitting diodes.
 3. The LED lightingsystem of claim 2 further comprising a time-based phase delay detectorto detect the phase delay of the phase modulated signal and generate thephase delay signal as a digital signal.
 4. The LED lighting system ofclaim 2 wherein the operating parameter is a peak voltage of the phasemodulated dimmer signal.
 5. The LED lighting system of claim 2 whereinthe phase delay signal indicates a dimming level and the controller isfurther configured to generate a switch control signal to cause theswitching power converter to respond to the dimming level indicated bythe signal without decreasing an effective resistance of the switchingpower converter, as perceived by a voltage source of the switching powerconverter, as the dimming level indicated by the signal increases. 6.The LED lighting system of claim 2 wherein the controller is furtherconfigured to generate approximately constant pulse widths for theswitch control signal during each cycle of phase modulated signal when aduty cycle of switch control signal is below the predetermined dutycycle threshold value.
 7. The LED lighting system of claim 2 wherein thecontroller is further configured to generate pulses for the switchcontrol signal during the phase delays of the phase modulated signal,wherein the pulse widths and duty cycles of the pulses of the switchcontrol signal generated during the phase delays are sufficient toattenuate ripple of the phase modulated signal during the phase delaysof phase modulated signal.
 8. The LED lighting system of claim 7 whereinthe pulses of switch control signal generated during the phase delayshave a period significantly greater than a period of the pulses of theswitch control signal during an active period of phase modulated signal.9. A method of controlling a light emitting diode (LED) lighting system,the method comprising: receiving a phase delay signal indicating a phasedelay of a phase modulated dimmer signal; determining a controloperating parameter from the phase delay signal using a signalprocessor; and generating a duty cycle modulated switch control signalusing the determined operating parameter to vary an input current to aswitching power converter with a phase modulated voltage and to maintaina regulated link voltage at an approximately constant value until a dutycycle of the switch control signal decreases to a predeterminedthreshold value and to decrease the regulated link voltage of theswitching power converter when the duty cycle of the switch controlsignal decreases to the predetermined duty cycle threshold value. 10.The method of claim 9 further comprising: receiving the switch controlsignal at a terminal of a switch in the switching power converter;converting the phase modulated dimmer signal into the regulated linkvoltage; and providing power to a load coupled to the switching powerconverter, wherein the load includes one or more light emitting diodes.11. The method of claim 10 further comprising: detecting the phase delayof the phase modulated signal using a time-based phase delay detector;and generating the phase delay signal as a digital signal.
 12. Themethod of claim 10 wherein the operating parameter is a peak voltage ofthe phase modulated dimmer signal.
 13. The method of claim 10 whereinthe phase delay signal indicates a dimming level, the method furthercomprising: generating the switch control signal to cause the switchingpower converter to respond to the dimming level indicated by the signalwithout decreasing an effective resistance of the switching powerconverter, as perceived by a voltage source of the switching powerconverter, as the dimming level indicated by the signal increases. 14.The method of claim 10 further comprising: generating approximatelyconstant pulse widths for the switch control signal during each cycle ofphase modulated signal when a duty cycle of switch control signal isbelow a predetermined threshold.
 15. The method of claim 10 furthercomprising: generating pulses for the switch control signal during thephase delays of the phase modulated signal, wherein the pulse widths andduty cycles of the pulses of the switch control signal generated duringthe phase delays are sufficient to attenuate ripple of the phasemodulated signal during the phase delays of phase modulated signal. 16.The method of claim 15 wherein the pulses of switch control signalgenerated during the phase delays have a period significantly greaterthan a period of the pulses of the switch control signal during anactive period of phase modulated signal.
 17. A light emitting diode(LED) lighting system comprising: a controller comprising: an input toreceive a phase delay signal indicating a phase delay of a phasemodulated dimmer signal; and a signal processor, coupled to the input,to receive the phase delay signal and determine a control operatingparameter from the phase delay signal and to generate a switch controlsignal using the determined operating parameter to control an inputcurrent in response to one or more values of the phase delay signal; andwherein the controller is further configured to decrease a duty cycle ofthe switch control signal as the dimming level decreases until thedimming level reaches a dimming level threshold and to keep the dutycycle of the switch control signal approximately constant for dimminglevels below the dimming level threshold.
 18. The lighting system ofclaim 17 further comprising a time-based phase delay detector to detectthe phase delay of the phase modulated signal and generate the phasedelay signal as a digital signal.
 19. A light emitting diode (LED)lighting system comprising: a controller comprising: an input to receivea phase delay signal indicating a phase delay of a phase modulateddimmer signal; and a signal processor, coupled to the input, to receivethe phase delay signal and determine a control operating parameter fromthe phase delay signal and to generate a switch control signal using thedetermined operating parameter to control an input current in responseto one or more values of the phase delay signal; wherein the controlleris further configured to increase an effective resistance of theswitching power converter as the dimming level indicated by the dimmingsignal decreases.